Solar Panels – Theory, Design and Production

Author: Timothy BoothDate: 30/07/10

Date Updated Reference Number change30/07/10 PLM-PSU-SolarReport-321-1.docx

Abstract

Solar cells make use of the photovoltaic effect; this is where incident light of certain wavelengths can cause electrons to be excited, break their bonds and be free to move around the material. The theory behind this phenomenon was then examined in detail. Available solar cells were then used in order to experimentally verify this theory. After this the characteristics of a 3x3 solar panel were calculated theoretically and then verified experimentally in order to prove the theory. This theory will then be used to predict the characteristics of the flight solar panels in the future.

Contents

(1.1) Introduction page 2(1.2) Aim page 2(2) Preliminaries page 2(3) How Solar Cells Work page 3

(3.1) Structure page 3(3.2) Solar Cell Process page 4(3.3) Dark Current page 6(3.4) Characteristic I-V Curve page 7(3.5) Spectral Corrections page 10(3.6) Intrinsic Resistances page 11(3.7) Variations with Temperature and Intensity page 13

(3.71) Temperature page 13(3.72) Intensity page 13

(4) Solar Panels page 14(4.1) Characteristic I-V Curve page 14(4.2) Losses page 16

(4.21) Mismatch Losses page 17(4.22) Hot Spot Heating page 18

(4.3) Prototype Panel page 18(5) Conclusion page 20(6) Future Goals page 20(7) References and Bibliography page 21

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(1.1) Introduction

Solar panels that are used to produce electrical power are called photovoltaic modules and are used both terrestrially and to power spacecraft. They are an advantageous source of power as they have a low power to weight ratio and low running costs. As well as this the solar radiation which is utilised by these modules is a long term power source. As a result solar panels are going to be used to provide power for the PLUME satellite, which is being built by the University of Leicester. The solar panels that will be used were originally going to be purchased Clyde Space. However, this option was not a viable one due to the large cost of the solar panels and so it is a necessity for the solar panels to be constructed.

(1.2) Aim

The eventual aim of the project is to construct the flight solar panels for CubeSat from the triangular advanced solar cells, which will be bought from Spectrolab. In order to make the solar panels that would be required for the satellite they would first need to be designed. However, in order to do this it would be necessary to understand how the characteristics of the solar panel depended on the characteristics of the component solar cells. In order to do this the theory behind how solar cells work would first have to be examined.

(2) Preliminaries

In order to prevent previous work from being repeated all documentation regarding solar cells was analysed, from the findings the time spent on each task could be prioritised in order for the maximum amount of new information to be gathered. However, very little work regarding the solar cells had been carried out previously and so it would be necessary to start from the basics and build the understanding from there.

Previous investigations have found the power required by the satellite, a total of 2.372W, and the amount of power that is expected to be produced by the TASC cells. A previous project, which was carried out by Thomas Searle and Chris Powell for their third year pair project, found that there would be a maximum total power of 2.949W whilst the satellite was in the sun. This is enough to power the satellite however it is only an approximation as the cut-outs for the detectors and the camera were neglected and the panels were assumed to be one large 10cm by 10cm TASC cell. This will not be the case as the TASC cells are small cut offs and so there will only be a finite number of them per solar panel with an overall area less than that assumed for the model, and so less power will be produced than predicted. Also the solar cells were not modelled exactly due to the lack of information of the materials within the cells. This meant that the cells were modelled as being made of gallium phosphide, whereas in actual fact they are a triple junction composted of indium gallium phosphide, indium gallium arsnide and germanium with a germanium substrate. Also only the top layer of this triple junction was taken into account when considering the reflectivity of the panels due to the complexity this would have added

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to the model. However the power the model produced is still a decent approximation as it takes into account how the output power varies with the angle of incidence of the incoming radiation and also the fact that the refractive index varies with the wavelength of the incident light. The solar flux and refractive index were both weighted to account for this.

(3) How Solar Cells Work

Solar cells utilise the phenomenon that is the photovoltaic effect. This is where incident electromagnetic radiation induces a current within certain materials. When solar radiation is incident upon a semiconductor the photons transfer their energy to the electrons within the valence band of the material. The electrons can then have enough energy to break their bond and become able to move freely through the lattice. This generates an electrical current within the material which can be carried out through an external circuit and dissipated in some useful way.

(3.1) Structure

Let us first consider a simple single p-n junction semiconductor solar cell. The p-n junction is formed by joining together a region which is doped in such a way that it has a higher concentration of electrons and a region which is doped so that it has a high concentration of holes. The result is to create an electric field across this junction that allows the exited electrons to not be recaptured and so a resultant current can flow. The p-n junction is usually very shallow, less than one micron.In order to carry the generated current through an external circuit there must be a metal contact on the surface of the solar cell. This contact has to leave most of the surface uncovered otherwise there will be no light incident upon the semiconductor and no current will be produced. However, the electrical resistance must not be too high. In order to achieve this, a “comb” shaped contact is commonly used. This is the case for the TASC cells as can be seen in Figure 1. The electrical contact on the dark side of the cell covers the whole back of the cell and in this case it has a protective layer beneath this with three small holes in order for the contact to be made. An antireflective surface is also usually applied to increase the amount of incident light absorbed by the solar cell.

Figure 1: An example of a “comb” shaped contact on the TASC

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(3.2) Solar cell process

When a solar cell is illuminated the following process takes place:

Photons which reach the interior of the cell and have an energy equal to or greater than the band gap are absorbed by the semiconductor and produce electron hole pairs which function as charge carriers.

The electric field or potential difference produced by the p-n junction separate these carriers before they can recombine. This results in a current and voltage in the external circuit.

The presence of a potential difference across the terminals of the device produced the phenomenon of injection and recombination of electron hole pairs. These are losses within the a solar cell and are dependant on the potential difference

When a load is connected to a solar cell which is then illuminated the current which flows is a summation of two components of internal current, these are:

a) The photogenerated current or photocurrent due to the generation of carriers by the light.

b) The dark current, due to the recombination of carriers driven by the external voltage. This voltage is needed to deliver power to the load.

As previously mentioned in a solar cell the carriers are produced by the absorption of photons, however, not all of photons incident on the solar cell are absorbed by the material and go on to produce these carriers. This is due to three effects:

1. The photons with energy below that of the band gap of the semiconductor are not absorbed. The losses due to this are called nonabsorption losses.

2. The semiconductor ahs a finite absorption coefficient, α, and thickness W. This therefore means that some photons which have energy greater than the band gap are still not absorbed. This gives rise to transmission losses with a transmission coefficient, τ, of the semiconductor.

3. Finally some photons are reflected off the surface of the semiconductor (caused by the difference in refractive index) causing reflection losses and a reflectance of the semiconductor, ρ.

As only one carrier pair is produced per photon absorbed an equation for the photogenerated current can be produced and is shown below.

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where α, is the spectral absorption coefficient, Ac is the area of the cell, e is the charge of an electron and S(E) is the number of photons incident on the solar cell with energy E.The transmission and reflectance losses can theoretically be set to zero to obtain a maximum photocurrent.

The nonabsorption losses cannot be set to zero as all semiconductors have a bandgap and so this is an intrinsic loss of the material.However this is not the full picture as some charge carriers are created far from the area of high electric field and then have to travel some distance towards it before being separated and collected across the junction. The fraction of these carriers which are collected before they eliminate each other is called the collection efficiency ηcol(E). This modifies the photocurrent equation, (see below). The collection efficiency should be a high fraction of the total amount of carriers generated, as those which are not collected do not contribute to the photocurrent.

Quantum efficiency is also an important parameter, it is split into two types, which are:

External quantum efficiency – This is the ratio of charge carriers collected by the solar cell to the number of photons of a given energy incident on the solar cell from the outside.

Internal quantum efficiency – This is the ratio of the number of charge carriers to the number of absorbed photons.

The internal quantum efficiency can be written as:

The graph (Figure 2) shows how quantum efficiency of the solar cells varies with the wavelength and hence energy of the incident light. The solar cells in question are the TASC cells which will be used on the flight solar panels. For photons with energy less than that of the band gap the solar cell is transparent. For high energy photons the

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carriers are produced close to the surface and so many recombine before being collected as photocurrent.

Figure 2: How the external quantum efficiency of the TASC cells varies with wavelength

(3.3) Dark Current

The external voltage which delivers energy to the load produces a bias across the solar cell and currents in the p-n junction even when there is no incident light. A positive bias across voltage increases the amount of minority carriers into both sides of the transition zone due to the reduction of the potential barrier of the junction. The minority carriers are then either recombined at the surface or within the bulk of the material to do this the carriers move via diffusion which creates a current within the solar cell.If the bias voltage is negative on the other hand there is reduction of the carriers both side of the transition zone due to the increase of the potential barrier across the junction. Thermal generation of electron hole pairs occurs and move around the external circuit which adds to the photocurrent when it exists, however this thermal current is negligible in comparison.The currents corresponding to the recombination current/diffusion current outside of the transition zone can be written as,

The current from recombination inside the transition zone can be written as.

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The total dark current is therefore the sum of the current inside and outside the transition zone

where m is a number between 1 and 2. At low voltages m tends to 2 and I0 tends to I02

and at high voltages m tends to 1 and I0 tends to I01.The current supplied by a solar cell to the load is the difference between the photocurrent and the darkcurrent. If we substitute in for the darkcurrent we find the overall current is given by the equation below. From this an I-V curve can be drawn.

The TASC cells have not yet been ordered and so to test the theory solar cells, of which nothing is known, will be used. By testing a single cell it should be possible to predict the behaviour of a solar panel under the same conditions which will be able to be verified by building said panel and testing it. This was the next step in the project.

(3.4) Characteristic I-V Curve

In order to produce a characteristic I-V curve, the current at short circuit, i.e. when there is no resistance, will be measured and then the solar cell will be connected to a variable resistor (the load) and the resistance gradually increased until there is no current passing through the resistor. The results were then recorded and the graph (Figure 3) produced.

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A graph to show the characteristic I-V curve of the solar cell

0

1

2

3

4

5

6

0 50 100 150 200 250 300 350 400

Voltage (mV)

Cur

rent

(mA

)

Figure 3: The characteristic I-V curve of the solar cell

By using the characteristic equation for the device it is possible to calculate some of the parameters of the solar cell. Using the assumption that m=1 (typical of normal operating conditions). At V=0 the exponential term tends to 1 which implies that the short circuit current equals the photocurrent. Also when the current is zero the exponential term is equal to the photocurrent. By applying these boundary conditions the value for I0 can be calculated. From the value of I0 the current and voltage at maximum power point can be calculated and hence the value of the maximum power.

At

At

A

8

With the values for IL I0 and VOC the values for the current and voltage at maximum power point can be calculated using the equations below.

Where

These equations gave values for the current and voltage at maximum power point as 4.97 mA and 0.272 V respectively. This implies that the maximum power point is the product of these two values gives a power of 1.35 mW.

Using this value for the maximum power point and by calculating the power incident on the solar cell using the intensity at the solar cell and the luminous efficacy of the light source, in this case a light bulb, the efficiency of the solar cell can be calculated, as shown below.

Where Ilux is the intensity of the light source in lux and ε is the luminous efficacy and A is the area of the solar cell. Using these two equations a value of 2.39% was calculated for the efficiency of the solar cell. This is a very low efficiency and it implies that the solar cells are broken.

(3.5) Spectral Corrections

The value that has been produced needs to be corrected as artificial light does not have the same spectrum as that of solar radiation (Figure 4), this correction is on going.

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Figure 41: Normalized spectral irradiance density for several optical sources

The luminous efficacy takes into account the efficiency of the light bulb as it requires a certain number of watts to provide the luminosity of the bulb. However, it does not take into account the differences between the two light sources spectra.The short circuit current can be corrected for by calculating a conversion factor to do this the following equation is used.

Where ISC(1a) is the short circuit current at an illuminance of one lux, ISC(AM1.5) is the short circuit current under standard operating conditions (air mass 1.5 with an irradiance of 1 kWm-2) and β is the conversion factor. The value of ISC(AM1.5) is usually given on the datasheet by the manufacturers, however, as no information is known about the solar cells used it may be necessary to take the solar cells outside in order to gain a rough estimate. For an irradiance of 1 kWm-2 incident upon the solar cell the light meter will have to read a value of 80 000 lux, this is obviously a very rough method but it is the only one available in order to take into account the differences in the spectra. After the conversion factor is calculated and assuming that the short circuit current depends linearly on the illuminance the following equation can be written.

Where ISC is the short circuit current of the solar cell and G is the illuminace of the light source in lux. By substituting in for ISC(1a) from the equation for the conversion

1 Short-Circuit current of solar cells under artificial light, Pablo Ortega, Santiago Silvestre and Luis Castañer, 22/07/2010

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factor the value for the short circuit current under normal operating conditions can be calculated using the following equation.

This conversion has not been completed for the solar cells used within the experiments outlined in this report as the value for ISC(AM1.5) is unknown and, due to the weather, has not been found experimentally.

(3.6) Intrinsic Resistances

This is only an approximation and the intrinsic resistive effects of the solar cell need to be taken into account in order for a better approximation to be obtained. These effects affect the external behaviour of the cell. The two main effects are the series resistance and the current leaks proportional to the voltage. The current leaks are usually characterised by a parallel resistance.The parallel resistance has its greatest effect when the voltage is lowest. This may be cause by:

Leakage around the edge of the cell Diffusion paths along dislocations Grain boundaries (where they exist) Small metallic short circuits

The parallel resistance is difficult to model; however, it has little importance under normal operating conditions.

The series resistance is important to the characteristics of the solar cell and is caused by:

Resistance of the metal contacts with the semiconductor The resistance of the layers of the semiconductor itself (in which lateral

currents might flow) The resistance of the metallic fingers which make up the front grid of the cell

These modify the characteristic I-V curve equation as shown below,

When the cell is short circuited the junction is biased by a voltage of value ISCRS. Therefore by using the value for the current at short circuit and its corresponding voltage (VSC), 5.23x10-3 A and 37x10-3 V respectively, the series can be calculated to have a value of 7.07Ω using the equation below.

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By applying the same boundary conditions as before two simultaneous equations are produced:

At

At

By assuming that ISC = IL an equation for I0 can be produced by solving the previous two equations simultaneously. The equation for I0 is shown below:

Using the new value for I0 and the previous value of 0.335 V for VOC and solving in the same way as before more accurate values for the parameters of the solar cells can be calculated, these are shown below (Table 1).

Parameter ValueCurrent at max. power point 4.78 mAVoltage at max. power point 0.272 V

Max. power point 1.30 mWEfficiency 2.29 %

Table 1: Values for selected parameters of the solar cell

The low value of the efficiency is either due to the difference in spectra between the sun and the bulb or the cells could be broken. Once the correction for the difference between the two spectra is done it will be known if the cells are broken or not.

(3.7) Variations with Temperature and Intensity

(3.71) Temperature

The photocurrent increases slightly with temperature partly due to the greater diffusion lengths of the carriers and partly due to the narrowing of the band gap

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allowing photons of lower energies to be absorbed. This improvement of photocurrent with temperature is always quite small. This modifies the characteristic equation as shown below.

It is clear to see that the current in the cell varies both through the exponential term and the I0(T) term. However the open circuit voltage also varies with temperature; as the temperature increases the voltage decreases. The decrease in the open circuit voltage outweighs the slight increase in the photocurrent. As a result of this the overall efficiency of the solar cell decreases.

(3.72) Intensity

The photocurrent of a solar cell is directly proportional to the intensity of the incident radiation. The open circuit voltage also varies with the intensity of the incident light. This implies that there will be an increase in efficiency due to the increase in open circuit voltage. The increase in the efficiency cannot continue indefinitely due to physical limits. These limits are not observed at low levels of illumination, however, if the illumination is increased sufficiently the ohmic losses due to the series resistance of the cell reduces the efficiently significantly.

By varying the intensity of the artificial light, measuring its intensity and plotting it against efficiency this statement could be experimentally verified. Again the differences between the spectra of the artificial light source and the sun need to be taken into account but the overall shape of the graph should be similar to that shown for the ideal case ( Solar Electricity: Engineering of Photovoltaic systems, E. Lorenzo, p85).By measuring the values of the shot circuit voltage and current and the open circuit voltage for each different value of intensity the efficiency could be calculated using the equations outlined in section (3.3). The intensity was varied by varying the distance between the light source and the solar cell. The luminous efficacy was calculated by dividing the luminosity of the bulb by the amount of power required to produce this luminosity. By using this value the power incident on the solar cell could be calculated and from this the efficiency, (i.e. the ratio between the power incident upon the solar cell and the output power of the cell). Figure 5, shown below, was the result of this experiment.

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A Graph to show how efficiency varies with incident power for a solar cell

0

0.5

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10 12 14

Incident Power (W)

Effic

ienc

y (%

)

Figure 5: A graph showing the variation of efficiency with incident power

As you can see from figure 5 the experimental curve matches that of the theoretical curve shown in the literature. The box shows the value of the incident power in low Earth orbit (LEO). It appears after the peak but is not much lower than it. This implies that the above statement is correct.

(4) Solar Panels

From the values of the parameters of the solar cells it should be possible to calculate the characteristics of a solar panel made from the same cells.

(4.1) Characteristic I-V curve

In order to generate the appropriate current a voltage for a certain application solar cells can be connected in series and parallel in what is called a solar panel, or photovoltaic module. It is quite difficult to predict the behaviour of a module as the equation for the characteristic I-V curve of the solar cell cannot be directly used. This is due to the fact that some parameters, especially IL and I0, cannot be measured directly. It is therefore necessary to develop an expression which gives the characteristics of the module from measureable parameters. It can also be difficult to predict the I-V characteristics of a photovoltaic module as the cells from which it is composed are not identical, due to imperfect manufacturing techniques, and so have different individual characteristics. This means that even if the characteristics of each cell are known it is still difficult to predict the characteristics of the module as a whole.However, this problem can be simplified using the following assumptions.

The effect of parallel resistance is negligible The photocurrent IL is equal to the short circuit current Isc

>> 1 under all working conditions

All of the cells are identical and function under the same conditions of illumination and temperature

Voltage drops in the conductors connecting the cells are negligible

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These assumptions result in very small errors however make calculating the characteristics of the module much simpler. It also makes it possible to use the previous equation for the solar cell to predict the characteristics of the solar panel. To do this the following must first be taken into account.

Where IP and VP are the current and voltage of the panel respectively and NS and NP

are the number of solar cells in series and parallel respectively. This means that the following expression can be written for the current of the panel.

Where

This equation is the equation for the characteristic I-V curve of a solar panel. However, the expression still contains the photocurrent and dark current which are hard to measure. Therefore it is necessary, using the above assumptions, to write an expression which only contains easily measureable parameters. This can be done as shown below.

From the assumptions the following expression can be written.

When I = 0, the open circuit voltage is given by the following

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By substituting the above expression for I0 back into the original formula a final equation can be written

This equation is quite useful as all of the parameters are known or are easily measurable. An inconsistency arises as I(V=0) ≠ ISC. But in all solar cells of practical use VOC >> IRS → I(V=0) ~ ISC.This equation, however, should, theoretically, be solved iteratively but a good approximation can be found by setting the current (I) term on the right hand side equal to ISC. This is also only an expression for a single solar cell and in order to solve for a solar panel the following must be taken into account, where ISCP, VOCP and RSP are the short-circuit current, open-circuit voltage and series resistance of the solar panel respectively.

This modifies the above expression into the solvable equation shown below.

(4.2) Losses

This assumes that all of the cells of the solar panel are identical and work under the same conditions, however, in reality this is not the case. Below are a couple of reasons for this variation between the solar cells.

Natural variation of parameters expected from any manufacturing process Variation of conditions across the solar panel, such as partial shading.

These can cause the following effects to happen

Mismatch losses, this is where the power generated by the solar panel is less than the sum of the power produced by the individual cells.

Hot spot heating, when a cell acts as a load to the others, either due to being shaded or broken. The power dissipated across this cell leads to an increase in temperature of said cell which, if hot enough, can irreversibly damage it.

(4.21) Mismatch Losses

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Most solar panels are made up of strings of solar cells connected in series, which in turn are then connected in parallel with other strings. The overall current is a summation of the current produced by the parallel part of the panel. It is therefore possible to reduce the mismatch losses by selecting solar cells with similar values of current at maximum power point (IM) and connecting them in series. This is a simple method which is effective in reducing mismatch losses and will therefore be used when constructing the solar panels.A second method to reduce the mismatch losses is to make intermediate connections between the cells, as can be seen in figure 6.

Figure 6: Intermediate connections on a 3x3 solar panel

This technique is, however, a lot more awkward to implement, especially when dealing with a small solar panel such as those being used for the satellite. There is also an increased probability of a bad connection between the solar cells. Therefore the first technique outlined will be used to reduce mismatch losses.

(4.22) Hot Spot Heating

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Intermediate connections

A solar panel is made by connecting solar cells together. Now consider if one of those cells has a significantly lower value of the short circuit current than the rest of the cells in the panel, caused by shading or a defective cell. This cell is thus subjected to a reverse bias and thus dissipates the power produced by the remaining “good” cells. This dissipation results in an increase in temperature of the “bad” cell and is local surroundings, creating a hot spot.In order to avoid these hot spots from occurring, bypass diodes are most commonly used. These diodes are connected in parallel to a series string of solar cells with its polarity reversed with respect to the cells. This is such that any reverse bias from the cells corresponds to the direct bias of the diode therefore providing a bypass for the current generated by the other cells. This reduces the amount of power the bad cell is able to dissipate and thus keeping the temperature down.The need for bypass diodes depends on, apart from the variation in the cell characteristics, the output voltage and the parallel resistance of the cells. However, as a general rule bypass diodes are a necessity if the output voltage is greater than 24V.Blocking diodes are often recommended to prevent the reverse current flow back from the battery through the solar panel when it is not illuminated. However for a 12V system and below more power will be lost through the diode than the solar panel. For a 24V or 48V system the losses will be much lower.As the CubeSat is a low voltage system and therefore losses need to be minimised there appears to be no need for bypass or blocking diodes within the solar panels.

(4.3) Prototype Panel

A solar panel made of 3 x 3 solar cells was made in order to experimentally test the theory previously outlined in this report. The first step was to make a frame on which the solar cells would be mounted. As the solar cells are not the ones being used for the flight panels there was no need to design a panel to the specification of the CubeSat frame. Therefore a wooden frame was used as this was the quickest and cheapest material to get hold of in the short period of time available. This does mean that a secondary prototype panel will need to be designed and investigated. This is the next step in the process.Once the frame was constructed the most complete solar cells were selected from the cells that were available. These cells were then submitted to the same conditions of illumination and the open circuit voltage and short circuit current and voltage were then noted in order for the value of the current at maximum power point (IM) to be calculated. After this was done the solar cells with the most similar vales of IM were connected together in a series of three. The three series strings were then connected together in parallel and glued to the frame. The equations outlined in section 4.1 were then used with the values of the short circuit current, voltage and open circuit voltage of the solar cell from section 3.6 to calculate the short circuit current, voltage and open circuit voltage of the solar panel for the same conditions. Hence the characteristic I-V curve could be produced. By assuming that the conditions within the dark room are a constant then the characteristic I-V curve predicted by the theory from the data produced by one solar cell under the same conditions could be experimentally tested.To do this the experimental set up used in section 3.4 was used again. The current and voltage for different resistances was then measured and plotted on the same graph as the theoretical I-V curve. This is shown in figure 7 below.

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The theoretical and experimental characteristic I-V curves of the prototype solar panel

00.0020.0040.0060.008

0.010.0120.0140.0160.018

0 0.5 1 1.5

Voltage, (V)

Cur

rent

, (A

)

TheoreticalExperimental

Figure 7: Theoretical and experimental characteristic I-V curves for the prototype panel

As is shown by figure 7 the two curves are similar, yet not exactly the same. This discrepancy can be put down to the fact that the theory assumed that all of the cells were identical whereas in reality this was not the case. However the curves are a close enough to conclude that the theory is correct.It is possible to calculate the current and voltage at the maximum power point of the solar panel and hence the maximum power point. To do this the following equations are used.

If the inequalities vocp > 15 and rs < 0.4 are satisfied then the following expressions are valid.

and

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Where

Using the values taken during the experiment values for the current and voltage at maximum power point of the solar panel were calculated to be 0.0164A and 0.786V respectively. By multiplying these two values together the power of the solar panel was found to be 0.0128W.

(5) Conclusion

This report gives an in depth background to the workings and characterisation of solar cells and solar panels. This is invaluable information which will allow for next tasks in the overall project to be completed with relative ease and completeness. Although there was insufficient time to start on the design of the flight solar panels the information and understanding gained from the undertaking of this short placement will be vital for this next step. As such it is the belief of the author that the aim of the project was completed.

(6) Future Goals

From this point the next step is to design and characterise a prototype solar panel from the TASC cells to the specifications and limitations of the satellite. This should be possible to be completed before the start of the autumn term 2010. A more detailed report will need to be written investigating the most feasible methods of connecting the cells together as well as to the satellite. As well as this viable cover glass material will need to be researched and sourced.

In order to help further the ability of the author with respect to the construction and design of the solar panels, and the progress of the CubeSat project, a fortnight long course in Switzerland focusing mainly on photovoltaics will be attended. This will give tuition in the construction of solar panels and hence improve the authors skills and confidence in building space worthy solar panels.

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(7) References and Bibliography

E. Lorenzo, Solar Electricity: Engineering of Photovoltaic Systems, p59-108, 1994

P. Ortega, S. Silvestre and Luis Castañer, Short-Circuit Current of Solar Cells under Artificial Light, 2003

http://www.reuk.co.uk/Diodes-and -Solar-Panels.htm, 23/07/10 Peter Fortescue, John Stark, Graham Swinerd, Spacecraft Systems

Engineering, 3, p325-354, 2003 Jet propulsion Laboratory, Solar Cell Array Design Handbook, 1, 1976

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